[PATCH] D23583: [AArch64] Add feature has-fast-fma

[James Molloy via llvm-commits]

jmolloy added a subscriber: jmolloy.
jmolloy added a comment.

Hi,

I also have concerns here. The TargetLowering hook states:

  /// Return true if target always beneficiates from combining into FMA for a
  /// given value type. This must typically return false on targets where FMA
  /// takes more cycles to execute than *FADD*.

Whereas you say:

  In spite of what the original author intended, I observed that the extra folds are worth it if FMA is as quick *FMUL* instead.

Which is correct? Or are you using this hook in a way the hook users don't intend? The wording used is vague and I really think we need to have more detail about what property of Exynos-M1 makes this good for Exynos but not for any other microarchitecture.

Cheers,

James


Repository:
  rL LLVM

https://reviews.llvm.org/D23583